On previously known presses (e.g., as disclosed in European Patent Application, EP 1 123 169 B1), a punch and a die of a pressing tool are moved against each other in a stroke direction until the punch meets the die or a plate arranged between the punch and the die. The resulting relative position of the die and punch forms a reference position from which the length of the die is determined. To this end, with the punch sitting on the die or on the plate supported by the die, the position of the punch end remote from the die must be detected.
This can be achieved by means of a detection unit that is activated as soon as the punch comes into contact with the die or the plate. The detection process is triggered by the rise in power consumption of the press drive connected with the action of the punch upon the die or plate. Accordingly, the control of a switching device for the detection unit is integrated in the press drive. The punch and die serve simultaneously as reference elements to detect their mutual reference position. If the position of the punch end that remote from the die is determined, then the punch length is calculated from this position and from the known position of the die surface impacted by the punch and, where applicable, from the known thickness of the plate between the die and the punch.
It would be advantageous to constructionally decouple the control of a detection unit to detect a mutual reference position of the tool parts from the functional machine components necessary for the regular machine operation.